More of Lessing: the Nobel-winning novelist at this year's Guardian Hay festival. Photograph: Martin Godwin

Doris Lessing has been a Nobel bridesmaid for so long that we'd all given up hope of her ever reaching the altar. She's also been a Booker bridesmaid three times - which is a measure, perhaps, of the ambivalence with which this literary titan is regarded in many quarters.

Even though, at 87, the best of her writing is probably behind her, it is wonderful that her importance should finally be acknowledged by the Swedish academy. For Lessing has done more than most writers to articulate the issues of the 20th century. In doing so - as several fans declared at a Guardian book club - she has changed lives.

Her greatest work is probably still The Golden Notebook, published in 1962, with which she cracked open the narrative certainties of the first half of the century to release a sexy and fractured female sensibility. But equally important are contributions to post-colonial literature, starting with The Grass is Singing, published in 1950. It was with this manuscript in her bag, and £20 in her purse, that she left her native Rhodesia for England in 1949.

Though she makes a famously good trifle when the socialising mood takes her, Lessing has never been one to ingratiate herself with any old person. Viewed from a hostile quarter, her career can be seen as a series of abandonments - of two of her three children when she left Rhodesia; of her communist beliefs in the 1950s; and, more recently, of any claim that she was ever a feminist. There are plenty of people who spit at mention of her name because they feel betrayed by her - though it's a mark of her power that so many take it so personally.

But her fearlessness about turning coat is linked to her ability to adapt and address each new era in its own terms and forms. She has done realism and modernism and science fiction, and has won different sets of fans with all of them. With Briefing for a Descent into Hell (1970), she developed a genre she described as "inner space fiction", a dizzying new way of depicting mental illness (and dramatising her distrust of the medical establishment).

She is a refreshingly uncosy presence in the pally world of literary London. Perhaps her biggest achievement is to end where she began - as an outsider, who, whatever her faults, could never, ever be parochial. A natural, then, for the international pantheon of the Nobel.